5 Most Common PoE Questions

Author: Brian Rhodes, Published on Feb 02, 2017

In our IPVM IP Networking course, Power Over Ethernet (PoE) is a core component that students show significant interest in.

The top ones are:

  1. Can I accidentally double PoE wattage by using midspans & switches together?
  2. Does each port produce max rated wattage?
  3. Can a cable plugged into a port, but not a camera, electrocute me or be a safety hazard?
  4. How far can PoE travel on a cable?
  5. Will cameras using power supplies be damaged by also plugging them into PoE ports?

In the sections below, we answer each question.

** ******* ** ********** ******, ***** **** ******** (***) ** * **** ********* **** students **** *********** ******** **.

*** *** **** ***:

  1. *** * ************ ****** *** ******* ** ***** ******** & switches ********?
  2. **** **** **** ******* *** ***** *******?
  3. *** * ***** ******* **** * ****, *** *** * camera, *********** ** ** ** * ****** ******?
  4. *** *** *** *** ****** ** * *****?
  5. **** ******* ***** ***** ******** ** ******* ** **** ******** them **** *** *****?

** *** ******** *****, ** ****** **** ********.

[***************]

Question: "*** * ************ ****** *** ******* ** ***** ******** & ******** ********?"

******: **. *** ******* ** ******* ***** *** ******** * negotiation ******* ***** * ****** ********** *** ******** *** ***** from * ****** **** * ****** ** ******* ********. ******* those ****** ******* ** *** ******* ***** **** ********* *******, they ** *** ********** ******* *** *** *****. ** **** way, *** '****' *** ******* ** *** ***** ** **** by *** ****** ******* ** *** *** ******* ****** ** security ******.

** ****** **** ******** ** ****** ******* **** ****** ************ *** ******** *** ********* ** **** ******.

Question: "**** **** **** ******* *** ***** *******?

******: ** ** *** **********. ***** * **** *** ** rated ** ******* *** *******, (**: **.** *** ***.*** ** 60W *** ***.***) *** ******* ** *** *** ** ******* it ******* ** *** ***** ****** ** *** ****** *** maximum ********* ***** *********. ** **** *****, ****** ******** ******, causing *********** ****** ** ******** ********** *** *** *******.

*** *******, **** ******** ***** *** ****** (****** **-*******) *** *** ********* ****** *****:

*** *** *** ***** ********* ** *** ****** ** ***. With * *** *****, **** *** ***** ** ******* ******* each, **: *** / * ***** = **.*** *** ****. However, *** *** *** ***** ********* *** **** ** ***** at **.** *** ***.*** ** **.* * * * = 61.6W. *** ********** ******* ******* **** ************** *** *** ****** power ********* ** *** ****** ** * **** *.**. **** means ** ** *** * ******* **** ******** *** ****, the ***** ****** ***** ** *********.

Question: "*** * ***** ******* **** * ****, *** *** * ******, *********** ** ** ** * ****** ******?"

******: **. *** ** *** ******* *********** *******, *** ***** is *** ******** ****** ****** * ********* ****** ******** **. This ***** **** * ***** ********* ** * *** ** not '***********' ** *** ***** ******* ** ** * *** device *** **** *** ******* * ****** ****** ******* ** incidental *******.

Question: "*** *** *** *** ****** ** * *****?"

******: *** ******* **** ********* ** *** ******** ******.* ********. By ******, ***** **** ****** ** *** ** *** ******* length ***** *** ** *********. ** *******, **** ******* ****** is **** *******, *** ***** ****** **** ******** ******** ****, ***** **** *** ******** **** ******** * **** ****' away **** *** ******, ****** *** ***** *** **** ***** travel ** *** **** ********* *****.

***** *** ** ***** *** *** *** ***** ********, *** distance ******* **** **** **** *** **** ******** *********, *** additional ******* **** *** ** ********* *** *** **** ******* warranties ** ****.

Question: "**** ******* ***** ***** ******** ** ******* ** **** ******** **** **** *** *****?"

******: *** ******, *** ******. ** **** *****, ******* ** other *** ******* **** *** ******* ***** **** **** ********* from * *** ** *** ****** ** ******* ********* ***** from * ***-******* ***** ******. *******, ********** **** ***** *** devices, ************ *** **** ******* ***** **** ** *** **** of ******** *** ******.

** *******, **** ** *** ** ***** **** ***** *******, but *** *********** ******* **** ********* ****** ** ******** ******.

PoE *** ************ ************* ** ******** **** ** ***** ** *******, *********** * separate ***** *** ****** *** *****. ** **** *****, * PoE ****** ******** **** ********* *** ***** ****** **** * single ****. *******, *** ***** ***-*** ******** ** ***** *** demand ********* ******, * ******** **** ****** * ******* ** often ****. ****:***: ****** **. ************* ***** *** ** ***** ************.

Comments (18)

"Can * ***** ******* **** * ****, *** *** * ******, *********** ** ** ** * ****** ******?" ******: **...

****'* *** *********** ****. ***** *** ****** ** ******** **** have ******* *** ** ***** **** ***** ** ** *********** happening *****. *** ******* ******* *** *** ******** ***** ********, if *** *** ** ********* ** * ****, ******* ** always ******* *** *** *** **** **, *** ** *** I **** ;)

******** **** *** ******* *** *** ******** ******* ** ****.

*'** ****** ******** **** *** ******* **** *** ***** ******* PoE. *** ***** *** ********** ** **? * **** ** see ** **** ******** ******** **** ********.

* ***** ** **** ** ******* ** **** ****** *************** of ***- ** ***** **** *** ***.***. ***** *** ********* in *** *********** ******* **** **** ************* *********** ***********.

**** **** ******* ** ******** ** *** ****, ** ** not ********* **** ********. ***** ** ***** * '***********' ******* that ******* **** *** ****** ******** ********** ***** ***** ** needs.

*** '***********' (**: ******** ****) ***, *** ******* *** ******** to *** *** **** *** ****** . ** *** ******** version *** ******* *** *** ****** ** **** ***.* ********* regardless. ***-******** *** ** ********* ****.

** **** ******, *** *** ***** (********** **** *** ** 100W ******** **** ******), ******* ******* ****** *****.

**** **** ******* ** ******** ** *** ****, ** ** not ********* **** ********. ***** ** ***** * '***********' ******* that ******* **** *** ****** ******** ********** ***** ***** ** needs.

****, ******** *** ****** ** ******* ***** ******** ********* * power ***** *** **********, * ******* **** *** ***** ***** 0, *** **** ***** ** ***** **** **** *** ** supplied.

********* **'* ****** ******* ***** *** ******* ******* *** ******** out ***** *** **** ****** ***'* **** ***** ** * difference ******* **** *** ********* *** ******* ***.

** **** ******* *** ** **** **** ****** **** **** you *** *** ****** ** ***'** ***** **** ** ******** system ******* ******* ****'* ** ***** *** ******* **** *** wire **** *** ** **-********* * *****. ** **** *****, you *** *** ************ ** *** *** **** *******'* ** possible ** **'* ********* *** **** *** *********.

...** **** *****, *** *** *** ************ ** *** *** this *******'* ** ******** ** **'* ********* *** **** *** standards.

****** *** **** ****** ** ******* * *** *** ****, which ***** ******* *** **** ;)

****** ***, ****, *** *** *** ******* ************, ** *** strict ***** ** *** **** ** *****.

**** ** *** ****** *** *** **** *****'* ******** ******* an ************ *******.

**** ***** *** **** *** * ****** **** ** ****, if *** *** ***** ****** ** ** * **** ***** when * **** ***** **.

******, * ****** **** **** *******. * **** ** **** my ******** *** ** ***'* *** **. * **** *** I've **** ******* ** *** *** ** ****** ** *** guard ***** ******** ** * **** ******.

*** *** ** ** ***** **** **** * **** **** in. ***** ** ** **** *****!

******* **'* *****. *** ****** **** *** **** *********** *********** stuff **** *** *** **** *** *** ****** ***** * and *, *** ***'** ***?

**** ***** **** **** - **** **** * *** **** PoE ****** **** * *********** ********** *** *** - **** kind ** **** *******

** ***** **'* (******) ******* **** ***** **** ****.

******* **********.

*** ****** **** ** ******* ** ******* *** *****? *** does *** ************ ****?

** **** ***** ***** * **** ** ****, ***** *** PSE ***** * ***** '*****' ****** ** ********* **** *.*** to *** ****** ** ** *** ******* ** ******* ***.

**** ***** ****** ** ********** ** *** ****/*** ** ******** if *** ************.

****** - **** ***** **** *****. ** ** ****** ** delivers * **** ****** ** ***** ** ******* ** **** the *** **********. ** **** ****** *** ************ *** *** switch **** ** ****'* ** *****.

****** ***** 👍🏻

** ** ****** ** ******** * **** ****** ** ***** by ******* ** **** *** *** **********. ** **** ****** its ************ *** *** ****** **** ** ****'* ** *****.

**, *** *******.

*** ****** ******** * ~** ***** ** **** *** ********** of *** ******.

** *** ********** ** ******* *** *** *** ***, ** either ********

  1. **-*** *** ** ** *** ** *** ****** ***********
  2. ** ******** ********** ****** ** *** ** ********* *** ***** class (** ***** ***** >* ** ********* ** *** ******), and **** ******** ***** ** **** *****.

** ****** ****, *** ****** *****'* ***** ******* ***** **** is ********. **** ** * ********* *******, **** *** ** cameras **** * **** ***** **** *** **** ***** *, so **** **** ** **** *.

***** ** * ****** ***** **** *********** **** *** ***** also, *** * *****'* *********** ** ** ********.

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